1. Field of the Invention
This invention relates generally to a data-projection unit for cameras which selectively projects a data pattern generated by a liquid crystal panel onto a photographic film, and is particularly concerned with a data-projection unit structure including a photographing light filter to permit overlay projection of a sharp data pattern onto the subject image formed on the film, regardless of the brightness level of the subject image being photographed.
2. Description of the Related Art
Conventional data-projection devices for cameras may not be able to project a sharp data pattern onto a photographed image when an especially bright subject is selected. In such cases, the data pattern may wash out or not even register on the exposed film. In order to prevent this shortcoming, camera manufacturers have proposed interposing a shielding plate between the photographic lens and the data-projection area of the photographic film into which the data pattern is to be projected. This shielding plate will protect the data-projection area from the photographing light when the shutter is activated. This does enable projection of sharp data patterns onto the data-projection area. However, because the data-projection portion of the film surface is completely shielded from the image being photographed, a new problem occurs in that the subject image is not projected at all within this region of the photosensitive film surface. Therefore, an undesirable "billboard" artifact (light colored data on an uniform black background rather than the subject image) may be formed on the film surface.
To reduce the occurrence of such artifacts, as disclosed in laid open Japanese patent applications H7-261257, H1-222245 and S56-7 4233, for example, it has been suggested to measure the brightness of the subject projected onto the data-projection area of the photographic film and to use a movable shielding plate to mask the data-projection area only where the level of brightness is sufficiently high (i.e. where the projected data would otherwise be visibly degraded or washed out). However, even here, the data-projection area is completely shielded when the brightness level exceeds a predetermined threshold, and so the aforementioned billboard artifacts may still be produced when a particularly bright subject is photographed.
Furthermore, implementation of these movable shield techniques requires use of a photometer or similar device for measuring the brightness of the subject immediately prior to or as the picture is being taken. These issues, coupled with the fact that a complex and potentially fragile electromechanical shield movement mechanism responsive to this photometer must be included within the camera body, foreclose implementation of such movable shields in the increasingly commercially significant disposable camera market.